The present invention relates generally to electro-optic materials and more particularly to an acoustic damping material for reducing acoustic modes in the electro-optic material.
Electro-optic material is a class of inorganic and organic crystals where the index of refraction of the material changes in response to electro-magnetic energy applied to the material. Such material may be used in the production of optical devices, such as optical switches, optical limiters, optical modulators and the like. In it simplest form, an optical signal, such as the output of a laser or the like, is launched into the electro-optic material having length and widths in the millimeter range and thicknesses in the tenths of millimeter range. The diameter of the optical path of the optical signal within the electro-optic material generally ranges from ten to a few hundreds microns across. Electrodes are formed on opposing surfaces of the electro-optic material that are parallel to the optical path of the signal passing through the electro-optic material. An electrical signal is applied to the electrodes which varies the index of refraction of the electro-optic material as a function of the variations of the electrical signal. The variations of the index of refraction of the electro-optic material alters the optical signal propagating through the electro-optic material.
The strength of the electric field distribution within the electro-optic material is a function of the distance between the opposing electrodes and the amplitude of the applied electrical signal. The strength of the electric field is the inverse of the distance separation of the electrodes. As the distance between the electrodes decreases, the strength of the electric field between them increases. As the distance decreases, the magnitude of the electrical signal can decrease to generate the same amount of change in the index of refraction.
Acoustic modes are generated in electro-optic material as a result of piezoelectric effects of electro-magnetic signals on electrodes connected to the electro-optic material. The piezoelectric effect changes the physical dimensions of the electro-optic material resulting in acoustic distortion that causes optical noise to be imparted in an optical signal generated by the electro-optic material. In an optical cavity, such as a Fabry-Perot cavity, the changes in the physical dimensions of the optical cavity causes variances in the resonance points of the cavity. This results in acoustic distortion that is imparted as optical noise in the modulated optical return signal generated by the Fabry-Perot cavity.
What is needed is an acoustic damping material that reduces acoustic modes in the electro-optic material. Further, the acoustic damping material should prevent unwanted external optical radiation from entering the electro-optic materials and internal optical radiation from exiting the electro-optic material at undesired locations.